Spectrograph with multiplexing of different wavelength regions onto a single opto-electric detector array

Abstract

An optical spectrograph utilizes a plurality of holographic transmission optical gratings operative to receive an incoming source of light to be analyzed and diffract the light such that different spectral components impinge upon spatially separated regions of an opto-electronic detector. Various grating configurations are disclosed, including a physical stack of gratings conducive to extreme compactness, as well as a spaced-apart configuration used to preclude spectral cross talk in certain configurations. Diverging light emerging from a fiber-optic bundle is collimated by a first lens assembly prior to passing through the gratings, and a second lens assembly is used to focus the diffracted light onto the detectors, preferably in the form of a two-dimensional CCD array.

We claim: 
     
       1. An optical spectrograph for use in analyzing a plurality of incoming light beams, comprising: a two-dimensional opto-electric detector array containing rows and columns of detector elements;   a plurality of holographic transmission optical gratings, each recorded to diffract a predetermined range of wavelengths, said gratings being supported so that each light beam to be analyzed passes through each, with each grating diffracting wavelengths of each beam in its range onto a different row of said detector array, resulting in multiple bands of radiation incident upon said array, each band having a height in pixels related to the number of incoming beams.   
     
     
       2. The optical spectrograph of claim 1 wherein said incoming light beams are arranged in a plane parallel to one another at least where they pass through said gratings. 
     
     
       3. The spectrograph of claim 1 wherein the recording of a particular grating alone causes the light diffracted by that grating to fall onto a particular set of detector elements comprising said array. 
     
     
       4. The spectrograph of claim 1 wherein the recording of a particular grating together with its physical orientation cause the light diffracted by that grating to fall onto a particular set of detector elements comprising said array. 
     
     
       5. The optical spectrograph of claim 1 wherein said gratings are substantially planar and stacked parallel to one another. 
     
     
       6. The optical spectrograph of claim 1 wherein said gratings are spaced apart such that light diffracted by each grating is re-directed so as not to pass through subsequent gratings. 
     
     
       7. The optical spectrograph of claim 1 where said opto-electric detector array comprises a charge-coupled device. 
     
     
       8. The optical spectrograph of claim 1 wherein said incoming light beams are carried by separate optical fibers. 
     
     
       9. The optical spectrograph of claim 1 wherein said incoming light beams are carried by separate optical fibers in a flat ribbon of such fibers. 
     
     
       10. The optical spectrograph of claim 1, further including means to collimate said incoming light beam. 
     
     
       11. The optical spectrograph of claim 1, further including means to focus the light diffracted by said gratings onto said detector elements. 
     
     
       12. In an optical spectrograph of the type including a holographic transmission optical grating operative to diffract light to be analyzed onto an opto-electric detector, the improvement comprising: means for simultaneously receiving a plurality of light beams to be analyzed;   said detector is in the form of a two-dimensional image sensor; and   a plurality of said gratings, each having a different line spacing and each exposed to each beam to be analyzed, and   means to direct the light of each beam diffracted by each grating onto a different surface area of said sensor.   
     
     
       13. The optical spectrograph of claim 12, wherein said for simultaneously receiving a plurality of light beams to be analyzed includes a ribbon of optical fibers, each carrying a different beam. 
     
     
       14. An optical spectrograph, comprising: a plurality of light sources to be simultaneously analyzed, the light from each source passing through a plurality of holographic transmission optical gratings, each grating being operative to diffract the light received at a different angle relative to the other gratings;   a two-dimensional image sensor; and   means for directing the light diffracted by each grating onto the surface of said sensor, whereby signals representative of different portions of the spectrum encompassed in the light from each source impinge upon said sensor in different areas.   
     
     
       15. The optical spectrograph of claim 14 wherein the different portions of the spectrum encompassed in the light from each source impinge upon said sensor as a series of separate bands having a height related to the number of sources, the width of each band being representative of a different spectral range. 
     
     
       16. The method of simultaneously spectrally separating a plurality of light beams, comprising the steps of: passing the optical radiation of each beam through a plurality of holographic transmission optical gratings, each grating diffracting a portion of the optical radiation of each beam using a different line spacing; and   focussing the diffracted light onto a planar image sensor so that the radiation diffracted by each grating falls on a different row of the sensor.   
     
     
       17. The method of claim 16 wherein the gratings are planar and supported parallel to one another. 
     
     
       18. The method of claim 16 wherein said gratings are oriented angularly with respect to one another so that the radiation from each grating falls on a different area of said sensor.